The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A compressor of a heating, ventilation and air conditioning (HVAC) system includes a motor that increases temperature of a refrigerant, such as freon, through compression. Oil within the compressor is used for lubrication of internal bearings and other motor components. The refrigerant changes from a gaseous state to a liquid state when the temperature of the compressor decreases below a threshold (e.g. 40° F.). The temperature of the refrigerant may decrease below the threshold, for example, when the compressor is in an environment with an ambient temperature that is less than the threshold and/or when the compressor is in an idle or OFF state. The refrigerant can mix with and dilute the oil when in a liquid state. This negatively affects properties of the oil and degrades lubrication of the motor components, as well as causes “slugging”. Slugging refers to attempts by the compressor to compress a refrigerant and/or oil in a liquid state. During slugging the compressor may operate erratically and inefficiently. Compressors are generally designed to compress a gas, not a liquid. Thus, decreases in refrigerant temperature below a threshold can negatively affect the operation of a compressor, as well as decrease the life span of compressor components.
To prevent oil dilution, a band heater may be applied to an exterior surface of a compressor crankcase. The band heater is used to heat the crankcase and thus a refrigerant contained therein. The band heater may be used to maintain the temperature of the refrigerant above a temperature at which the refrigerant changes from a gas to a liquid.
A first example band heater assembly includes a cable and a stainless steel tube that has fingers that extend laterally from the tube. The cable extends through and is contained within the stainless steel tube. The fingers are used to transfer heat generated by the cable to a compressor crankcase. The fingers have sharp edges, which raises handling and ergonomic issues. This band heater assembly exhibits a limited amount of heat transfer from the cable to the compressor crankcase.
A second example band heater assembly includes a first end and a second end. A resistive element extends from a first end to the second end and back to the first end. In other words, the resistive element has two passes over the length of the band heater assembly. The ends include rivets, washers, and brackets, which are used to connect the band heater assembly to a crankcase. Use of the rivets, washers, and brackets increases assembly complexity and material costs. Also, the rivets and washers tend to interfere with the crankcase and cause gaps between the band heater assembly and the crankcase. The gaps reduce heat transfer efficiency and can create hot spots at the ends of the band heater assembly. Portions of the band heater assembly that are not in contact with the crankcase increase in temperature due to lack of heat transfer. This can over time degrade the band heater assembly in the hot spot areas.
The second band heater assembly is also limited in application to an object that has a consistent outer diameter and/or perimeter shape for the lateral width of the band heater assembly. As an example, an object that is cylindrically shaped may have a consistent outer diameter and/or perimeter shape, whereas a spherically shaped object has an inconsistent outer diameter (i.e. diameters of vertical or lateral cross-sectional slices through the sphere) with respect to a band heater assembly. An inconsistent outer diameter and/or perimeter shape can cause buckling and gaps between the band heater assembly and the object, which can also result in hot spot areas.